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March 24, 1931. R. H. KRUSE STRING GALVANOMYETER Filed Jan. 6,' '195o/NVE/vToR ArmRNEY indicated at 11?.-and120. `Theinvention may,

PatentediMar, 24, 1931 i I .Y

' steine aanvraag-@METER Application filed January 6', ,Serial No.418,691.

The presentV invention relates to string gal vanometersy Itis lan objectof the present invention to improve vupon string galyanometers, toy theend thatjtheir weightand size may be dei crea'se d,th `e`ir portabilityenhanced and their f costv "of manufacture'. lessened'. 'Cther andfurther objects will be explained hereinafter',

and'` will be' particularly pointedf out, in the appended claims.

@ai system.

- string galvanometer embodying the present invention; Fig, 2 isn avsectionV upon the *line -2- 2 of Fig. 1, lool;ing in the directionoffthe arrows; Figiffis an enlarged Yiragmen'` taryyiewI ofthe-stringmember; and Fig lv yis a diagrammatic sectional view of va cammagnet.or'.electromagnet,V shown `O-shaped,` 'i and havingtwo slightlyspacedpolel pieces" 16.'y The energizingcoilsgfor the ymagnetiare of; courge,be used also in'other types of gal- `l3`ebruary 19, 1929, the* type*s'liown' inthe only,k '1tl may bey stated, however, that thevillustrative galyanometer is of very muchv` smaller size. The trameisxcontinu'ous', or?r I ..O-shaped, providing a double-magnetic rei' jThis, with `the ,centrally dis-l turn circuit.

Withtl'ie above' ends inview, a feature' of i l the inyention residesin'u using a conductive f string member that is `rvery thin, exceptthat" 1 v the portion'of the string. member that is dispose/'dinthejp'atho the light beam'issuf-f iiciently thick so that Vitsosoillationsymay' readily beV observed with the ordinary opti#The;inventili win nwjbe more] 'fuiiy Xs plained in connection with theaccompanying drawings, in whichFig. 1 isa View of The pole pieces;

vpermits.;economy weight without proper` tionate loss oflmagnetfstrength.

iinwroan, Assisnon no Tian onMBR-IDGE iN- ,atconcpoitn'rion on NEW"Thefstring `member I5 is suspended inthe electromagneticl` fieldproduced `in the re-.

kstricted air gap kbetween the slightly spaced pole .pieces 16, and`atthe focusv ofthe beam of "lightrays that. proceed from al lamp orother Sou of light 2, through tubes ,22?111761 j v23, J O alight-'sensitive in a ,ph O i' graphm Camera 31 Shownfsutably Positionedin-Fig'lfllj The light fronitl'ie lamp 2 is con; Y

densed by a condenserlsystemand is focused? onV ythe 4 string member byVay microscope,"y 17,

and "isprojected' to the cameral by fa lens systenfiy 24.Theinagniiication maybe from Q Qto 1,000 `times. Inelectrocardilography', `i'forV examplait may be 500fti`mes.

The string member 1 5 is shown in EZV as c arriedby-"ia base,:frame'orsupport '12.

@ne end'fof the' stringm'ember 15 is secured to supportingv head oranchorage 'member 38 andthe other to a supporting head orailchoragemember), the former being stationyary upon the vframe 12andthe other adj ust-'- able.` The adjustable head 89 is yieldingly butlirmly held in `adjusted position' byk spring 46. .The` adjustment ofthe movable head 39 isA eii'ected by means of a yscrew 40 thaltmayb'eturned by a thumb wheel 14. By reason of the various adjustments,andthe positions of the anchorage membersSS and 89' above and-beloy`vthesmallspace between the pole `pieces 16, it is'possible to adjust thektension of the string membery 15, Lso as tostretch it lengthwiseVoitself between the anchorage members, andto position an inso Ytermediate portion o tthefstring member at n the Alproper point inthesaidsmall space,

. l l 'e' z be Vanometers, such las are illustrated, for eig-ftransvelsey ,lO-the mlgnetl Hug twee? im? ample, `i'n the above-namedlpatent, for :in j

United States Patent No. 1,702,650; grantee@ The string of suchv `aVga'lva'noineter is fordi- Anznrily constituted of a quartz orf glassthread, -verythinlycoatedvwith gold or other metal drawings' being for'illustrative" 'purposes to render it*condu'ctiVe. The measurementsobtained with such instruments depend for Y their accuracy upon the.exceedinglyslight,l sidewise or transverse movement ofthe'elec- 4trofconductiverv string member, in respo'nse to 5 exceedingly 'smallchangesv in current therein. n

`posed arrangement'l ofthe coils 11 and 20,V`'Notwithstalndingthe'thinnessfof theinetal whole strinO fore, thestring member 15 ismadeof evenY less than ordinary thinness, sogas torender 1t as light as possible. So thin a string member .would leave noappreciablertrace or line upon the film-29 ofthe camera 31. The stringmember is, therefore, slightly thickened, `orV made of largercrossxsection, at an interme-VV 15' diate point 18, where it is disposedbetween 1 the slightly spaced pole pieces V16. The'extremely thin stringmember is. easilyactu-k ated by the magnetic field, andthe enlarged orbelted portion 'leaves just as effective a shadow upon the sensitivefilm as though the form thickness throughout.

The length of the vbeltedportion need not be very great.,A Aone-millimeter length is suflicientto c'astthe requiredl shadow on thefilm 29. In practice, however, it is possible` to use longer belts,evenl belts extending Y throughout the full width of the polefaces'.

Thus, a belt one-eighth inch long on a string member ltwo and one-halfinches long open.

ates very satisfactorily. So small a belt does not appreciably `changethe period of vibration of the unbelted stringA member, noi-itsstiffness, so that the string member operates almost exactly the same asthough itwere unbelted, and the sensitivity of the resulting" instrumentis of the same order as that prevailingin the very much'largerV and moreexpensive galvanometers. The longer the extent of the enlarged section,the greateris the weight of the resulting strinof member t: Vb b 7andthe less marked become the advantages described herein. In practice,therefore, it is preferable to have the enlarged section as small aspossible, say, of substantially the same length, or but slightly largerthan, the width of the beam of light rays at the point where the stringmember is positioned between the pole pieces. p 'Y V The 4novel stringmember may be made in many ways, as by bombardment by cathodiosputtering, with shields placed on both sides of the portion of thestring member to be belted; ror by condensing organic material on thestring from the vapor form; or by'ap.-` plying a lacquer film; orrbydissolving away, on each side of the'belted portion, the coatV ingof anordinary string member havingits coating throughout its length. A veryeffective way isv to lower the string member into a drop of electrolyte,and to electroplate on the 4string member a. length equal to the lengthof the drop. By controlling the length of the drop, it is possible tocontrolithe length of the belt; and the diameter of thebelt is afunction of the current and the time. Vea-.1V

iember were of the same unirecording the shadow produced rious'metalsmay beused, such as copper and gold c Avery small'Einthoven galvanometeris thus provided, that will give good photo- 'i graphic reproduction,even. on veryV fast, transverse movements of the string member. 'Becauseof the thinness ofthe string, the galvanometer does not lose insensitivity, and the belt produces a satisfactory shadow. In-

deed, because of the thinl nature of thestring member, the period ofvibration may be yeven higher than in present-day galvanometers.

. Modifications will also occur to persons skilled in the art, and allsuch areconsidered to fall within the'spirit and scope of the invention,as definedin the appended claims.

` l. In a string galvanometer, an electroconductive string member.having an intering opposed slightly', spaced pole pieces,

and an electro-conductive 'string member stretched-lengthwiselof itselfwith a portion y'of the string vmember, positioned in the space betweenthe poley pieces transversely'to the path of the magnetic flux betweenthe pole pieces, means forproducing a beam of light. traversing thespace between the pole pieces, and means for receiving or recording thevshadow produced by the string 'member in thebeam of light, theportion'of the string member in the beam ofnlight being of enlarged crosssection, and the enlarged cross section being of substantially the samelength as the width ofthe beam of light at the point where the stringmember is positioned between the pole pieces. e l

'4. In a string galvanometer, a magnet having opposed slightly spacedVpole pieces, two anchorage members disposed respectively above and belowthe space between the pole pieces, an electroconductive string memberthe ends ofwhieh arecarried by the anchorage members so that the stringmember is stretched lengthwise of itself between the anchorage members,with `a portion of the Ystring member positioned in the space betwen thepole piecesntransversely to the path. of themagnetic flux between thepole pieces, the said portion of the'string member being of enlargedcross section, means for producing a beam of light traversing the spacebetween the pole pieces, and means for receiving or by the string memberin the beam of light.

5. In a string galvanometer, an O-shaped magnet having opposed slightlyspaced pole pieces, centrally disposedY energizing coils, two anchoragemembers,disposedrespectively Y; above andbelow the'space between thepole pieces, an electro-conductive string member Y the ends of whicharecarried by theanchorage members l,so that` the'string member is ystretched lengthwise of itself between the anchorage membersgwith aportion of thel string member ositioned Ain fthe space ,be-k tweenthepole pieces transversely to the path .p ofthe magnetic flux betweenthepole pieces',k y

the said portion of tliestring memberl being of enlarged cross section,means for producing a beam of light traversing the vspace between thepole pieces, and means for receivingor recording the shadow produced bythe A string member in the beam of light.

In testimony whereof, I have Vhereunto subscribed my. name.

. RALPH H. KRUSE.,

